1. Field of the Invention
The present invention relates to a mobile terminal, and more particularly to an ear/microphone connection circuit in a mobile terminal for connecting the mobile terminal with an ear/microphone that includes a call switch connected to an ear-microphone line.
2. Description of the Related Art
An ear/microphone (i.e. an earphone/microphone), which has a call switch to receive, send or end a call, is widely used for hands free communication with a mobile terminal. The ear/microphone includes a speaker (i.e. an earphone) and a microphone, which are hereinafter referred to as an “ear-speaker” and an “ear-microphone”, respectively. When an ear/microphone is connected to a mobile terminal, a user can hear audio outputted from the terminal and input audio to the terminal using the ear/microphone, instead of using a microphone and a speaker mounted on the terminal. To connect the ear/microphone to the mobile terminal, the ear/microphone has a plug and the mobile terminal has a corresponding ear/microphone jack. If the user inserts the plug of the ear/microphone into the ear/microphone jack of the mobile terminal, an ear-speaker and an ear-microphone of the ear/microphone are electrically connected to an ear/microphone connection circuit in the mobile terminal.
The ear/microphone connection circuit checks whether the ear/microphone is connected to the mobile terminal. When the ear/microphone is connected to the mobile terminal, the ear/microphone connection circuit receives an audio signal, outputted from the ear-microphone of the ear/microphone, from an ear-microphone line connected to the ear-microphone, and outputs an audio signal, which will be outputted through the ear-speaker of the ear/microphone, to an ear-speaker line connected to the ear-speaker.
The ear/microphone includes a call switch called a “send/end button”. The user pushes the call switch when he or she wishes to receive an incoming call, to send an ongoing call or to end a call. The call switch can also be used to redial a recently dialed number. To accomplish this, the ear/microphone connection circuit in the mobile terminal also detects a switching operation of the call switch.
FIG. 1 is a circuit diagram showing a conventional ear/microphone connection circuit 106 in a mobile terminal, to which an ear-microphone 102 in an ear/microphone 100 is connected. This figure does not show a mechanical structure for connection between the ear/microphone 100 and the ear/microphone connection circuit 106, in which a plug of the ear/microphone 100 is inserted into an ear/microphone jack, allowing the ear/microphone 100 to be electrically connected to the ear/microphone connection circuit 106. This figure also does not show an ear-speaker in the ear/microphone 100, and a portion of the ear/microphone connection circuit 106 whereby an audio signal is outputted to the ear-speaker of the ear/microphone 100. The configuration of the plug and ear-speaker are known to those of ordinary skill in the art.
The ear-microphone 102 in the ear/microphone 100 is connected in parallel with a call switch 104 for receiving an incoming call, or sending or ending a call, as described above. When the plug of the ear/microphone 100 is not inserted in the ear/microphone jack, a switch 110 in the ear/microphone connection circuit 106 is switched to a connection terminal Pb. On the other hand, when the plug of the ear/microphone 100 is inserted in the ear/microphone jack, the switch 110 is switched to a connection terminal Pa. The connection terminal Pa is connected to an ear-microphone line 108, which is connected to the ear-microphone 102 in the ear/microphone 100 when the ear/microphone 100 is connected to the ear/microphone connection circuit 106. The connection terminal Pb is connected to an inverting input (−) of a comparator 112 for detecting whether the ear/microphone 100 is connected to the circuit 106.
The comparator 112 is driven by power source VPD. A capacitor C2 and a resistor R3 are connected between the inverting input (−) of the comparator 112 and ground. A non-inverting input (+) of the comparator 112 is connected to a connection node between two resistors R1 and R2 that are connected in series between the power source VPD and ground. A reference voltage Vref, divided according to the resistance ratio of the resistors R1 and R2, is inputted to the non-inverting input (+) of the comparator 112.
The voltage of power source VPA is dropped via two resistors R4 and R5 connected in series, and the dropped voltage is applied to a common terminal of the switch 110. A capacitor C3 is connected between ground and a connection node between the resistors R4 and R5. The common terminal of the switch 110 is connected to an inverting input (−) of the comparator 114 for detecting a switching operation of the call switch 104 in the ear/microphone 100, and it is also connected to an ear-microphone terminal Ear_Mic for the ear/microphone 100. The ear-microphone terminal Ear_Mic is connected to a codec (coder-decoder) (not shown) that receives and processes an audio signal outputted from the ear-microphone 102. For example, if the mobile terminal is a CDMA (Code Division Multiple Access) mobile terminal, the ear-microphone terminal Ear_Mic is connected to a codec such as is provided in Qualcomm's MSM (Mobile Station Modem) chip (not shown).
The comparator 114 is driven by the power VPD. A capacitor C1 is connected between the inverting input (−) of the comparator 114 and ground. A non-inverting input (+) of the comparator 114 is connected to a connection node between the two resistors R1 and R2 connected in series between ground and the power source VPD. The reference voltage Vref, divided according to the resistance ratio of the resistors R1 and R2, is inputted to the non-inverting input (+) of the comparator 114.
The power source VPA supplies power for driving an analog circuit of the mobile terminal, whereas the power source VPD supplies power for driving a digital circuit of the mobile terminal. For example, each of the power sources VPA and VPD provides a supply voltage of 2.8 Volts. The resistances of the resistors R1 and R2 are determined so that the reference voltage Vref is, for example, 0.25 Volts.
The ear/microphone connection circuit 106 employs two resistors R4 and R5 to drop the supply voltage (for example, 2.8 Volts) by about half (for example, to 1.5 Volts), and supplies the voltage-dropped power as ear-microphone bias power to the ear-microphone line 108, so as to prevent distortion of an audio signal from the ear-microphone 102. When the ear/microphone 100 is connected to the ear/microphone connection circuit 106, the switch 110 is switched to the connection terminal Pa, thereby allowing the ear-microphone bias power to be supplied to the ear-microphone 102 via the ear-microphone line 108 connected to the ear-microphone 102.
When the plug of the ear/microphone 100 is not inserted in the ear/microphone jack, the switch 110 is switched to the connection terminal Pb. In this case, the comparator 112 outputs a “low” signal since ear-microphone bias power of a voltage higher than the reference voltage Vref is inputted to the inverting input (−) of the comparator 112. Under this condition, if the plug of the ear/microphone 100 is inserted into the ear/microphone jack, the switch 110 is switched to the connection terminal Pa. This causes the comparator 112 to output a “high” signal since the ear-microphone bias power is not inputted to the inverting input (−) of the comparator 112. A signal outputted from the comparator 112 is applied to a controller (not shown) of the mobile terminal via a comparison signal terminal Comp1. For example, if the mobile terminal is a CDMA mobile terminal, the controller is Qualcomm's MSM chip. Based on the signal outputted from the comparator 112 via the comparison signal terminal Comp1, the controller, to which the output signal is applied, determines whether the ear/microphone 100 is connected to the mobile terminal.
While the plug of the ear/microphone 100 is inserted in the ear/microphone jack, and thus the switch 110 is switched to the connection terminal Pa, the comparator 114 detects a switching operation of the call switch 104 in the following manner. If the call switch 104 is in an off position (i.e. open), the comparator 114 outputs a “low” signal since ear-microphone bias power of a voltage higher than the reference voltage Vref is inputted to the inverting input (−) of the comparator 114. Under this condition, if the user presses the call switch 104 to turn it on, the comparator 114 outputs a “high” signal since the ear-microphone bias power is not inputted to the inverting input (−) of the comparator 114. As with the signal outputted from the comparator 112, a signal outputted from the comparator 114 is applied to the controller of the mobile terminal via a comparison signal terminal Comp2. Based on the signal outputted from the comparator 114 via the comparison signal terminal Comp2, the controller detects the switching operation of the call switch 104.
The ear/microphone connection circuit as described above uses the ear-microphone bias power also as power for detecting the switching operation of the call switch. However, a voltage for detecting the switching operation of the call switch may be lower than a voltage for biasing (or driving) the ear-microphone since a voltage needed to detect the switching operation of the call switch is at a level where it is just detectable by the comparator, which is different from a voltage needed to bias the ear-microphone.
It is necessary to supply power for detecting the switching operation of the call switch even when the mobile terminal is in a sleep mode. This is because if the user turns on the call switch even when the mobile terminal is in a sleep mode, the mobile terminal must detect the turning on of the call switch to shift to an idle mode. On the other hand, it is not required to supply power for biasing the ear-microphone when the mobile terminal is in the sleep mode since the ear-microphone is not used in the sleep mode.
However, even when the mobile terminal is in the sleep mode, it continues to supply the ear-microphone bias power, which is used to detect a switching operation of the call switch. Accordingly, the ear-microphone bias power will provide an unnecessarily high voltage to forms a current path via the ear-microphone 102 of the ear/microphone 100. Accordingly, compared to when the ear/microphone is not connected to the mobile terminal, standby power consumption increases when the ear/microphone is connected to the mobile terminal, thereby reducing the standby time and battery life.